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A mealybug on a cassava stem
A mealybug on a cassava stem
Pascaline Minet

GENEVA — Between a mission in Ethiopia and a meeting in Rome, Hans Herren stops over in Geneva to speak at a conference at the World Trade Organization. The Swiss agricultural engineer is a world-renowned expert in insects who has spent most of his professional life in Africa. During the 1980s and 90s, he established a massive program to combat an insect that destroyed yuca (also called manioc, or cassava) crops. The project is credited with averting famine for literally millions of people.

Herren, 66, now devotes most of his time promoting “green” agriculture techniques to the public and to politicians. For his efforts in that domain, he was awarded the 2013 Right Livelihood Award — also known as the “alternative Nobel Prize” — given to distinguished individuals who work on environmental or development issues.

Born in 1947, Herren grew up in Vouvry in southwestern Switzerland, where his father had a tobacco farm. He continued his studies in agricultural engineering at the Zurich Engineering School, where he specialized in entomology, the study of insects. Then he went to the University of California at Berkeley for two years to deepen his knowledge of organic insect control — an approach that consists of fighting agricultural pests with their natural predators, usually other insects.

“After my studies, I didn’t really feel like returning to Switzerland, because the opportunities for developing organic pest control systems seemed limited,” he remembers. “So I went to Africa, sort of looking for an adventure.”

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Entomologist and agricultural engineer — Photo: WTO

When Herren arrived at the International Tropical Agriculture Institute in Nigeria, there was a major food security threat hanging over the continent. An insect called the cassava mealybug was attacking the tuber that provided most of the nutrition for 200 million Africans. The cassava mealybug was accidentally introduced to Africa by scientists, and didn’t have any natural predators in Africa — so it was spreading quickly. Insecticides didn’t work, and breeding a naturally-resistant variety of yuca would take years.

Good killer wasps

That’s the context in which Herren started his one-man battle against the mealybug that made him famous, and for which he was awarded the World Food Prize in 1995. First, the agricultural engineer and his colleagues tried to identify an insect in nature that was a natural predator of the mealybug.

“If such an insect existed, it would have to live in some part of Latin America, because that is the native region for yucas and for the mealybug,” he explained. After several unsuccessful attempts, the researcher finally found, in Paraguay, parasitic wasps that laid their eggs in the mealybugs’ abdomen and killed them.

They couldn’t just release the wasps in Africa without taking some precautions. The wasps were quarantined in a lab in London for several months, where Herren and his colleagues verified that they did in fact attack the cassava mealybug specifically, and that they didn’t carry viruses. “There is always a risk when you introduce a new species into an environment where it is not native,” Herren admitted. “But we carried out all possible experiments to minimize that risk.”


The first tests at the beginning of the 1980s, in infested fields in Nigeria, produced excellent results. A couple of months after the introduction of the natural enemies, the mealybug populations plummeted. They then stabilized, at a low level. Thanks to that experience, Herren convinced the Interafrican Phytosanitary Agency to deploy his wasps on a large scale over the entire continent.

That’s when another adventure started for the agricultural engineer. The areas infested by the mealybug were so vast that the wasp releases had to be done by airplane. These were often quite eventful: “We were shot at over Ghana, and another time, we were forced to land in Tanzania, because they thought we were spies,” Herren remembers with a grin.

Around 1.6 million wasps were released as part of the program, which lasted from 1982 to 1993 and covered 24 countries in the “yuca belt,” which extends from Senegal to Mozambique. Since then, populations of both the mealybug and the parasitic wasp have remained low and stable, making the project an undeniable success.

“The program developed by Hans Herren was based on a relatively classic concept in organic pest control, which is to introduce the natural enemy of the pest,” explained Marc Kenis, a researcher at CABI, a research center based in Delemont that specializes in organic pest control. “The impact he had on food security is especially notable.”

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Nigerian farmers — Photo: Mike Blyth

In fact, according to the the World Food Prize Jury, Herren saved the life of around 20 million people with his project.

But Herren is modest about his accomplishments. “At the time, there was a problem with the mealybug, and I did my best to find a solution. I was particularly satisfied that we were able to prove that you can solve serious agricultural engineering problems with simple, environmentally friendly solutions,” he said.

A pilgrim's march

His experiences have made Herren a strong advocate of sustainable agriculture, based on agricultural techniques that respect the environment, like organic pest control, but also crop rotation and green fertilizer. He believes that the world urgently needs to turn its back on the agricultural techniques that took root in developed countries and some developing countries (such as India) after World War II. “That agriculture, based on large amounts of fertilizer and pesticides, has led to an increase in production but it has also caused serious pollution and has destroyed the soil fertility,” he explains.

Herren also refused to consider GMOs a solution for increasing crop yields, due to their cost and uncertainties about their effect on the environment. “It seems illogical to try to create new organisms, when we are not doing anything to protect the agricultural biodiversity that already exists and is disappearing rapidly,” he says.

[rebelmouse-image 27087543 alt="""" original_size="300x225" expand=1]

Cassava production in Nigeria — Photo: USAID

Philipp Aerni, a specialist in agricultural policy and development at Herren’s alma matter in Zurich, who has been researching yuca varieties for several years, does not agree with Herren’s assessment. “Organic pest control worked well against the mealybug, that is true, but there are other pests against which that technique does not work. It is necessary to imagine other solutions, and I think that discarding biotechnologies out of principle is a mistake.” In fact, a research group at his university is developing a GMO yuca that would be resistant to certain viruses.

In 2005, Herren left his job as the director of the International Center for the Physiology and Ecology of Insects, based in Nairobi, Kenya, after working there for 11 years. Since then, he has worked full-time promoting sustainable agriculture, particularly through the Biovision foundation, which he started in 1998. Based in Zurich, Biovision works to promote the spread of sustainable agricultural techniques among small farmers in East Africa.

Herren was co-president of the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD), an initiative that brought 400 researchers together for two years to discuss solutions to feeding the planet’s population.

The IAASTD’s report was made public in 2008, and the experts pointed to both organic agriculture and ecological agricultural methods as the routes to follow to guarantee the world’s future agricultural needs. “Why don’t the majority of countries follow this model of agricultural development, even though it is supported by the experts? Probably because of resistance from agricultural companies, who do not want the system to change,” Herren says.

But the entomologist refuses to get discouraged. He takes the time to relax when he can at the organic farm he owns in California with his American wife — then he picks back up the pilgrim's baton, and resumes his journey to promote sustainable agriculture around the world.

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